Add new lint macro_no_longer_exported (#1031)

Addresses checkbox in
#946

---------

Co-authored-by: Predrag Gruevski <[email protected]>

src/lints/macro_no_longer_exported.ron

@@ -0,0 +1,45 @@
+SemverQuery(
+    id: "macro_no_longer_exported",
+    human_readable_name: "macro is no longer exported",
+    description: "A macro_rules macro that was previously exported is no longer exported.",
+    required_update: Major,
+    lint_level: Deny,
+    reference_link: Some("https://doc.rust-lang.org/reference/macros-by-example.html#path-based-scope"),
+    query: r#"
+    {
+        CrateDiff {
+            baseline {
+                item {
+                    ... on Macro {
+                        name @output @tag
+                        public_api_eligible @filter(op: "=", value: ["$true"])
+                    }
+                }
+            }
+            current {
+                item {
+                    ... on Macro {
+                        name @filter(op: "=", value: ["%name"])
+                        # Check the macro still exists but is no longer public API
+                        # and isn't doc(hidden) (which would be caught by another lint)
+                        public_api_eligible @filter(op: "!=", value: ["$true"])
+                        doc_hidden @filter(op: "!=", value: ["$true"])
+
+                        span_: span @optional {
+                            filename @output
+                            begin_line @output
+                        }
+                    }
+                }
+            }
+        }
+    }"#,
+    arguments: {
+        "true": true,
+    },
+    error_message: "A macro that was previously exported with #[macro_export] is no longer exported. This breaks downstream code that used the macro.",
+    per_result_error_template: Some("macro {{name}} in {{span_filename}}:{{span_begin_line}}"),
+    witness: Some((
+        hint_template: r#"{{name}}!(...);"#,
+    )),
+)

src/query.rs

@@ -1095,6 +1095,7 @@ add_lints!(
     inherent_method_must_use_added,
     inherent_method_now_doc_hidden,
     inherent_method_unsafe_added,
+    macro_no_longer_exported,
     macro_now_doc_hidden,
     method_parameter_count_changed,
     module_missing,

test_crates/macro_no_longer_exported/new/Cargo.toml

@@ -0,0 +1,7 @@
+[package]
+publish = false
+name = "macro_no_longer_exported"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]

test_crates/macro_no_longer_exported/new/src/lib.rs

@@ -0,0 +1,22 @@
+// No longer exported but not hidden - should trigger
+macro_rules! example_macro {
+    () => {
+        println!("Hello from macro!");
+    };
+}
+
+// No longer exported but is hidden - should NOT trigger (caught by different lint)
+#[doc(hidden)]
+macro_rules! will_be_hidden {
+    () => {
+        println!("Will become hidden");
+    };
+}
+
+// Now exported - should not trigger
+#[macro_export]
+macro_rules! internal_macro {
+    () => {
+        println!("Internal macro");
+    };
+}

test_crates/macro_no_longer_exported/old/Cargo.toml

@@ -0,0 +1,7 @@
+[package]
+publish = false
+name = "macro_no_longer_exported"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]

test_crates/macro_no_longer_exported/old/src/lib.rs

@@ -0,0 +1,20 @@
+#[macro_export]
+macro_rules! example_macro {
+    () => {
+        println!("Hello from macro!");
+    };
+}
+
+#[macro_export]
+macro_rules! will_be_hidden {
+    () => {
+        println!("Will become hidden");
+    };
+}
+
+// Internal macro - should not trigger when made public
+macro_rules! internal_macro {
+    () => {
+        println!("Internal macro");
+    };
+}

test_outputs/query_execution/macro_no_longer_exported.snap

@@ -0,0 +1,28 @@
+---
+source: src/query.rs
+expression: "&query_execution_results"
+snapshot_kind: text
+---
+{
+  "./test_crates/declarative_macro_missing/": [
+    {
+      "name": String("will_no_longer_be_exported"),
+      "span_begin_line": Uint64(1),
+      "span_filename": String("src/lib.rs"),
+    },
+  ],
+  "./test_crates/macro_no_longer_exported/": [
+    {
+      "name": String("example_macro"),
+      "span_begin_line": Uint64(2),
+      "span_filename": String("src/lib.rs"),
+    },
+  ],
+  "./test_crates/macro_now_doc_hidden/": [
+    {
+      "name": String("becomes_non_exported"),
+      "span_begin_line": Uint64(36),
+      "span_filename": String("src/lib.rs"),
+    },
+  ],
+}

test_outputs/query_execution/macro_now_doc_hidden.snap

@@ -11,6 +11,13 @@ snapshot_kind: text
       "span_filename": String("src/lib.rs"),
     },
   ],
+  "./test_crates/macro_no_longer_exported/": [
+    {
+      "name": String("will_be_hidden"),
+      "span_begin_line": Uint64(10),
+      "span_filename": String("src/lib.rs"),
+    },
+  ],
   "./test_crates/macro_now_doc_hidden/": [
     {
       "name": String("will_be_hidden"),

test_outputs/witnesses/macro_no_longer_exported.snap

@@ -0,0 +1,20 @@
+---
+source: src/query.rs
+description: "Lint `macro_no_longer_exported` did not have the expected witness output.\nSee https://github.com/obi1kenobi/cargo-semver-checks/blob/main/CONTRIBUTING.md#testing-witnesses\nfor more information."
+expression: "&actual_witnesses"
+snapshot_kind: text
+---
+[["./test_crates/declarative_macro_missing/"]]
+filename = 'src/lib.rs'
+begin_line = 1
+hint = 'will_no_longer_be_exported!(...);'
+
+[["./test_crates/macro_no_longer_exported/"]]
+filename = 'src/lib.rs'
+begin_line = 2
+hint = 'example_macro!(...);'
+
+[["./test_crates/macro_now_doc_hidden/"]]
+filename = 'src/lib.rs'
+begin_line = 36
+hint = 'becomes_non_exported!(...);'